This undoes commit 
14ce0cb411c88681ab8f3a4c9caa7f42e97a3184.
Since jbd2_journal_start_commit() is now fixed to return 1 when we
started a transaction commit, there's some transaction waiting to be
committed or there's a transaction already committing, we don't
need to call ext4_force_commit() in ext4_sync_fs(). Furthermore
ext4_force_commit() can unnecessarily create sync transaction which is
expensive so it's worthwhile to remove it when we can.
http://bugzilla.kernel.org/show_bug.cgi?id=12224
Signed-off-by: Jan Kara <jack@suse.cz>
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>
Cc: Eric Sandeen <sandeen@redhat.com>
Cc: linux-ext4@vger.kernel.org
 static int ext4_sync_fs(struct super_block *sb, int wait)
 {
        int ret = 0;
+       tid_t target;
 
        trace_mark(ext4_sync_fs, "dev %s wait %d", sb->s_id, wait);
        sb->s_dirt = 0;
        if (EXT4_SB(sb)->s_journal) {
-               if (wait)
-                       ret = ext4_force_commit(sb);
-               else
-                       jbd2_journal_start_commit(EXT4_SB(sb)->s_journal, NULL);
+               if (jbd2_journal_start_commit(EXT4_SB(sb)->s_journal,
+                                             &target)) {
+                       if (wait)
+                               jbd2_log_wait_commit(EXT4_SB(sb)->s_journal,
+                                                    target);
+               }
        } else {
                ext4_commit_super(sb, EXT4_SB(sb)->s_es, wait);
        }